Over the past several years, there has been a growing interest in optical communications. Experimental systems have been installed and evaluated and commercial installations have been planned in several areas of the country.
Two types of cables are used in optical communications, one including a plurality of fiber lightguides which are generally arranged in ribbons and in arrays, and another which is a single lightguide fiber. The single lightguide fibers have been used to interface electrical and optical apparatus such as, for example, regenerators and signal coders and to provide optical patch cords and jumper cables for a main distributing frame.
Each of the above-described cables has its own distinct connection technology. In making a single, fiber-to-fiber connection, end portions of the two lightguide fibers to be spliced together must be aligned coaxially such that end faces of the opposing fibers are in a predetermined relationship to each other. This is important, particularly since signal losses which are introduced by axial misalignment and end separation are synergistically cumulative.
A single fiber lightguide connector may be one such as that shown on pages 89-90 of an article by T. L. Williford et al entitled "Interconnection for Lightguide Fibers" published in the Winter 1980 issue of the Western Electric Engineer. The basic elements of the connector are a single fiber within a cable sheath that provides protection and mechanical strength, a plastic conical plug at the end of the fiber with the fiber centered inside the plug and a biconical sleeve which accepts two plugs and causes the alignment of the axes of the fiber ends. The biconical alignment sleeve is a precisely molded part which includes two truncated conical cavities that control the end separation and axial alignment to the end faces of the fibers which are encapsulated within the plugs that are seated in the conical cavities of the sleeve.
In the fabrication of a jumper cable, a single fiber cable is cut to length, and the jacket of the cable is removed from a short length at the cable's end to expose the protruding glass fiber. The coating on the fiber is removed and a precision metallic sleeve is slid over the fiber and the inner and outer cable jackets and crimped around the inner jacket. Then the conical plug is molded concentric with the fiber axis and the metallic sleeve is crimped about the strength member and outer cable jacket so that any tension applied to the cable is transferred to the strength member. The circular symmetry of the conical design provides precise axial alignment of the fiber lightguide cores. Following molding, the plug must be precisely sized to control plug end separation within the biconical alignment sleeve. This is accomplished by grinding the plug length to a tolerance of about .+-.0.00075 cm. After grinding to size, the fiber end may be polished to provide an optically smooth surface with the plug length remaining substantially constant.
Interconnection requires that the ends of the lightguide fibers be smooth, flat and perpendicular to the fiber lightguide axis and the lightguide axis to be coincident with those of the plugs and the biconical alignment sleeve. End preparation methods which have been used include polishing, sawing, controlled breaking, and manual lapping. The use of an index matching material between fiber ends in a splice may also be used to reduce the signal loss due to reflections and surface imperfections in the end faces of the fibers. A "bend and score" technique for single fiber end preparation is described by J. F. Palgleish in an article entitled "A Review of Optical Fiber Connection Technology" published in the Jan. 31, 1977 issue of Telephony magazine.
There is a need for methods and apparatus for the rapid preparation of lightguide fiber ends that are encapsulated in conical plugs in a repetitively controllable fashion to facilitate the factory and/or field connectorization of single fiber lightguide cables. This need is not met by any known apparatus and while the presently used techniques may be used, the elements of control and speed are lacking.